The overall objective of this research proposal is to provide direct evidence that bacterial lipopolysaccharide (LPS) affects both T and B lymphocytes in gut-associated lymph-oreticular tissue (GALT). It will be shown that the interaction of LPS with GALT T cells results in a subpopulation which can be induced by thymic dependent antigen to become mature T suppresor (Ts) cells, while interaction with GALT B cells results in the induction of a mature population which includes precursor cells for IgA responses. For these proposed studies, we will employ unique mouse models including: 1) LPS responsive C3H/HeN and syngeneic LPS nonresponsive C3H/HeJ mice; 2) germfree (GF, LPS-free) C3H/HeN and C3H/HeJ mice and their conventional (Conv.) counterparts; and 3) X-linked immune deficient (xid) mice with either CBA/N, C3H/HeJ or C3H/HeN backgrounds. GALT T cell subpopulations from C3H/HeN and C3H/HeJ mice will be compared for numbers and intensity of Thy- 1.2+, Lyt-1+, and Lyt-2+ cells by FACS analysis. In another series, GALT T cells from LPS responsive mice (and C3H/HeJ as controls) will be treated with LPS in vitro and assessed for phenotypic conversion. Phenotypic conversion will also be investigated in vivo after chronic oral administration of LPS to GF C3H/HeN mice and assessment of antigen inducible Ts cells in vivo and in vitro. LPS effects on GALT B cells, with emphasis on IgA precursors, will be determined by comparison of GF and Conv B cell subpopulations for maturation markers including surface immunoglobulin (sIg), I-A, complement receptor (CR), and Lyb differentiation antigens. GF mice, which have been shown to exhibit immature B cell subpopulations, will be induced to maturation by chronic gastrointestinal exposure to LPS, and LPS induced B cell maturation in these mice will be assessed by induction of IgA responses. The relationship between LPS sensitivity and the ability to induce oral tolerance will be studied at both the T and B cell level in GALT using C3H/HeN and C3H/HeJ xid and normal mice. By using offspring from appropriate matings, T helper (Th) cells for IgA responses will be induced in the presence of either immature or normal B cell subpopulations. Furthermore, the induction of B cell tolerance in the presence of either Th or Ts cell populations will be studied.
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